The invention relates to a spindle assembly used to rotate and hold a machine tool or workpiece. Such an assembly normally comprises inner and outer coaxial shafts having front and rear ends and extending along a common axis with the inner shaft being axially displaceable in the outer shaft, a holding assembly on the front ends adapted to grip a tool or workpiece in an axially forwardly displaced position of the inner shaft relative to the outer shaft, a coupling ring fixed on the rear end of the outer shaft, and an actuator having a piston axially engageable with the rear end of the inner shaft and operable to axially shift the inner shaft in the outer shaft.
The actuator is typically coupled to the ring by an arrangement comprising an array of two-arm levers each of whose one arm can hook into a groove on the ring. The other arm of each lever has a foot that is radially outwardly angled so as to present radial inner and outer surfaces which are parallel to each other but which extend at an acute angle to the shaft axis. The inner surfaces engage in a groove that is formed on the release device. In order to pivot the hooks out of the groove of the coupling ring there is an axially displaceable ring that can engage the outer surfaces of the levers. When the ring is moved axially back, it slides on the outer surfaces and pivots the other arms out, decoupling the ring from the actuator.
Such an arrangement is quite complex and must be specially constructed so as not to open when the spindle assembly is rotated at high speed.